You can put this solution on YOUR website! In trapezium PQRS, PQ is parallel to RS. If Angle P=120 degrees, find the measure of Angle S.
I assume you are British since the British trapezium is USA's Trapazoid and the USA Trapezium has no parallel sides.
Now since PQ is parallel to RS, PS and QR are traversals and Angle P + Angle S equals 180 degrees so Angle S is 60 degrees